Spatial filters are used in laser systems and other optical systems to improve beam quality and/or to restrict the range over which the beam wanders, either in the angle of propagation or in displacement from an intended beam axis. Further, the spatial filters can be used to partially restrict a “focus pull” in which a beam waist translates along the beam propagation direction, and may, for example, come sufficiently close to the location of an optical surface to cause damage. Spatial filters can limit one or two dimensions and can be implemented to produce various aperture shapes, for example, square, rectangular, circular, ovular, or other aperture shapes.
Serious problems may arise when an attempt is made to spatially filter high-power laser beams. Damage can occur to the material constituting the spatial filter itself. For example, when the laser beam is powerful enough, it can melt or evaporate the material constituting the spatial filter. The high power beam can drill new holes wherever it lands and can effectively enlarge the aperture and reduce or eliminate the spatial restriction that the filter was meant to impose. This can limit both the utility and lifetime of the spatial filter, not to mention potentially limiting the lifetime of other nearby optical or electronic components. The nearby optical or electronic components can be damaged or destroyed by the unwanted deposition of the melted or evaporated spatial filter material or scattered incident laser beams. Illustrative components that can be damaged by either route include, for example, vulnerable surfaces of other optics, mounts, and enclosure walls.
In view of the foregoing, spatial filters with improved tolerance toward high-power lasers and other electromagnetic radiation sources would be of significant interest in the art.